The most likely outcomes in order for me is:
Berto by KO
Guerrero by decision
Guerrero by KO
Berto by decision

Berto should be able to overcome the skill differential by landing hard shots on The Ghost. Guerrero has been hurt and discouraged by much smaller men, and Berto is one of the better punchers at welterweight. I wouldn't be surprised if Berto gave away the fight though.

I am leaning towards Berto. I personally think Guerrero is overall a better fighter but he has jumped so many weight classes that it takes away from that. I have a few questions about how Berto has recovered from his first loss but Guerrero probably lacks the power at welterweight to test that. My pick would be Berto by decision.